back of the knee problem

[Deleted User]

Recently been spending time on my knees at work (Primary teacher) and have developed problems as a consequence. Now, I experience discomfort when kneeling. Had it checked out by physio and he says there is no evidence of any problem, muscular or skeletal. Hasn`t affected running but have been unable to do significant gym work.
Love to hear from anyone who can shed light on this mystery injury.